Stars are present both during day time as well as during night time. Because of the bright light of the Sun, the stars are not visible during day time.

(i) Comets : Comets are also members of our solar system. Comets are celestial bodies that revolve around the sun in highly elliptical orbits. However, their period of revolution round the sun is usually very large. A comet appears generally as bright head with a long tail. The length of the tail of the comet grows in size as it approaches the sun. The tail of a comet is always directed away from the sun.
(ii) Meteors : At night, when the sky is clear and the moon is not there, you may sometimes see bright streaks of light in the sky. These are commonly known as shooting stars, although they are not stars. They are called meteors. A meteor is usually a small heavenly object moving around  the sun. Occasionally, a meteor enters the earth's atmosphere. At that time it has a very high speed. The friction due to atmosphere heats up meteor. It glows and evaporates in a very short time. That is why the bright streak appears for a very short time.
(iii) Meteorites: Some meteors are so large that a part of them reaches the surface of earth before they evaporate completely. These are called meteorites. Meteorites help scientists in investigating the nature of the material from which solar system was formed.

Halley's comet appears periodically after every 76 years. It was last seen in 1986. So it will be visible again in the mid of 2061.

We always see the same side of the moon because the moon does not rotate (i.e. spin at its own axis) like the Earth does, so we only see the side that faces us and this side faces at us all the time.

Sketches are shown as given below:
                  

The axis of rotation of the Earth is not perpendicular to the path of its orbit, but it is slightly tilted. The tilt is responsible for the change of seasons on the earth.

Halley's comet appears periodically after every 76 years. It was last seen in 1986. So, it will be visible again in the mid of 2061.

No, some are dim (yellow) while some are bright (white).

There are eight planets in our solar system:
(i) Mercury (Budh) : It is nearest to the Sun. It is the smallest planet of our solar system. It is very difficult to visualize because it is near to the Sun. It has no satellite.
(ii) Venus (Shukra) : It is nearest to the Earth. It is the brightest planet. It is also called as morning and evening star due to its appearance. It also has no moon or satellite. It rotates from East to West.
(iii) Earth (Prithvi) : The earth is the only planet where life exists. It has special environmental conditions, right distance from the Sun, so has right temperature, presence of water and blanket of ozone that makes life possible here.
(iv) Mars (Mangal) : It is the first planet outside the orbit of the Earth. It appears reddish, so is called red planet. It has two small natural satellites.
(v) Jupiter (Brihaspati) : It is the largest planet. It rotates very rapidly on its axis. It has large number of satellites. It also has faint rings and large moons.
(vi) Saturn (Shani) : Saturn is yellowish in colour. It has beautiful rings. It has large number of satellites. It is least dense, density is less than water.
(vii) Uranus and Neptune: They are outermost planets of our solar system. Uranus rotates East to West, and has high rotation speed

We know that (time period)2  ∝ (radius of orbit)3
\({ T }_{ 1 }^{ 2 }={ Kr }_{ 1 }^{ 3 }\)                     . . . (i)
\({ T }_{ 1 }^{ 2 }={ Kr }_{ 2 }^{ 3 }\Rightarrow { T }_{ 2 }^{ 2 }=\left( \frac { { r }_{ 1 } }{ 2 } \right) ^{ 3 }\)          .... (ii) \(\left[ \because { r }_{ 2 }=\frac { { r }_{ 1 } }{ { r }_{ 2 } } \right] \)
\(\frac { { T }_{ 1 }^{ 2 } }{ { T }_{ 2 }^{ 2 } } =\frac { { r }_{ 1 }^{ 3 } }{ { r }_{ 1 }^{ 3 } } \times 8\)
⇒ \({ T }_{ 2 }^{ 2 }=\frac { { T }_{ 1 }^{ 2 } }{ 8 } \)
⇒ \({ T }_{ 2 }=\frac { 1 }{ 2\sqrt { 2 } } \)
It means that time period reduces by \(\left( \frac { 1 }{ 2\sqrt { 2 } } \right) \) factor.
So, the days in a year will be approx. 129 instead of 365 days.